A method for treating electroplating wastewater

Abstract

The application relates to a kind of electroplating wastewater treatment methods, belong to wastewater treatment technical field.The application removes insoluble impurities and heavy metal ions in wastewater by primary coagulation, complex-oxidation and secondary coagulation, and then removes organic matters in water by anaerobic / aerobic process and membrane bioreactor technology.The treated electroplating wastewater can reach the discharge standard stably.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, and more particularly to a method for treating electroplating wastewater. Background Technology

[0002] Electroplating is a key process in electronics and semiconductor manufacturing, and plating solutions containing complexing additives (such as ethylenediaminetetraacetate and pyrophosphate) are widely used. These additives form stable metal-complexes with heavy metal ions, which greatly increases the difficulty of wastewater treatment.

[0003] For electroplating wastewater containing high concentrations of additives, traditional solutions mainly rely on physicochemical precipitation. This method, in order to break down the stable structure of complexes, necessitates the addition of excessive amounts of complex-breaking agents, flocculants, and other chemical reagents, leading to high treatment costs and the generation of large amounts of chemical sludge, causing serious secondary pollution. Simultaneously, the effluent heavy metal concentration fluctuates greatly, making it difficult to consistently meet standards. While biological treatment technology can degrade some organic additives, the high concentrations of heavy metal ions in electroplating wastewater are highly toxic to microorganisms, resulting in extremely poor microbial tolerance. Direct biochemical treatment strongly inhibits microbial activity, leading to low treatment efficiency and a high risk of system collapse.

[0004] Existing single treatment routes cannot simultaneously meet the requirements of stable compliance, low reagent consumption, and no secondary pollution. There is an urgent need for a new technology that can efficiently treat electroplating wastewater containing high concentrations of additives. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for treating electroplating wastewater.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a method for treating electroplating wastewater, comprising the following steps: S1. Adjust the pH of the electroplating wastewater to 8-10, add ferrous sulfate and stir for the first time, add flocculant and stir for the second time, let it stand and then filter. S2. Adjust the pH of the electroplating wastewater to 2-3, add an oxidant and stir for the third time; the oxidant includes hydrogen peroxide. S3. Adjust the pH of the electroplating wastewater to 7-9, add metal capture agent, coagulant and flocculant and stir for the fourth time, let it stand and then filter. S4. The filtered electroplating wastewater is subjected to anaerobic / aerobic denitrification treatment, followed by membrane separation and filtration in a bioreactor, and then disinfection to obtain the treated electroplating wastewater.

[0007] The electroplating wastewater treatment method of this invention mainly includes the following process flow: a primary coagulation tank, a complex-breaking oxidation tank, a secondary coagulation tank, an anaerobic / aerobic process, and a membrane bioreactor. The electroplating wastewater first passes through the primary coagulation tank. In the primary coagulation tank, ferrous sulfate can reduce high-valent heavy metal elements (such as hexavalent chromium) in the wastewater to generate trivalent iron. Trivalent iron forms ferric hydroxide colloid in an alkaline environment, which, together with polyacrylamide, forms flocculation precipitates, removing most of the insoluble suspended pollutants in the wastewater. This reduces the COD and heavy metal content of the wastewater entering the complex-breaking oxidation tank, thereby reducing the demand for oxidizing agents in the complex-breaking oxidation tank and metal scavenging agents in the secondary coagulation tank, and improving removal efficiency.

[0008] Subsequently, in the complex-breaking oxidation tank, H2O2 is used to catalyze the reaction of complexed heavy metals and residual ferrous sulfate in the wastewater in an acidic environment to generate an active series of HO·. On the one hand, the complexed parts are oxidized and decomposed into small-molecule organic acids or alcohols, and on the other hand, the heavy metals in the wastewater are removed from the complexed state and transformed into a free state, so as to facilitate the subsequent coagulation and precipitation of heavy metals and the biochemical treatment of organic matter.

[0009] Subsequently, in the secondary coagulation tank, metal scavenging agents, coagulants, and flocculants are added. The metal scavenging agents can form stable insoluble substances with heavy metals in the wastewater. The purpose of adding coagulants is mainly to neutralize, adsorb, and bridge the insoluble suspended matter formed after oxidation and recapture of the wastewater through the interaction of the coagulants and the wastewater, thereby destabilizing the pollutants and forming flocs. The flocculants are then used to aggregate the flocs into large particles and precipitate, thereby further removing heavy metals from the wastewater.

[0010] The wastewater is then treated using an anaerobic / aerobic (A / O) process. This process creates alternating anoxic and aerobic environments, utilizing the synergistic effects of nitrification and denitrification by different microbial communities to remove nitrogenous pollutants. After the anaerobic / aerobic treatment process degrades organic matter in the water, the mixed liquor is pumped or gravity-driven, allowing water to pass through a bioreactor membrane (MBR) and be discharged. Activated sludge and macromolecules are retained by the membrane, achieving filtration and separation of activated sludge and water. Finally, further disinfection yields the treated electroplating wastewater.

[0011] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S1, the first stirring time is 25-35 min, the second stirring time is 10-15 min, and the settling time is 15-25 min. By reasonably setting the time parameters for coagulation reaction and sedimentation, it is ensured that large and dense flocs are formed and efficient mud-water separation is achieved. If the stirring time is too short, the reagent dispersion and reaction will be insufficient; if the stirring time is too long, the already formed flocs will be sheared and destroyed, resulting in a decrease in sedimentation performance. If the settling time is too short, the solid-liquid separation will be incomplete; if the settling time is too long, the treatment time will be increased and the efficiency will be reduced.

[0012] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S1, the flocculant includes one or more of polyacrylamide and chitosan; the amount of ferrous sulfate added is 400~800 ppm based on the total amount of electroplating wastewater; and the amount of flocculant added is 400~800 ppm.

[0013] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, the third stirring time in step S2 is 50-70 minutes. This stirring time ensures that the oxidant and wastewater fully contact and react, achieving efficient complex breaking.

[0014] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S2, the amount of oxidant added is 400~2000 ppm, calculated based on the total amount of electroplating wastewater. Adding an appropriate amount of oxidant can effectively destroy the structure of metal complexes and release the complexed heavy metals.

[0015] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S3, the metal scavenging agent includes one or more of xanthate, dithiocarbamate, and sodium sulfide; the coagulant includes one or more of ferrous sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum chloride, polyferric sulfate, polyaluminum chloride, and polyaluminum ferric chloride; and the flocculant includes polyacrylamide. Based on the total amount of electroplating wastewater, the amount of metal scavenging agent added is 400-1000 ppm; the amount of coagulant added is 200-1000 ppm; and the amount of flocculant added is 20-100 ppm. Using the above-mentioned combination of agents, through the synergistic effect of chelation precipitation, coagulation, and flocculation, residual free and complexed heavy metals in the wastewater can be deeply removed.

[0016] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S3, the fourth stirring time is 10-30 min, and the settling time is 5-15 min. By controlling the stirring and settling times, the metal capture, coagulation, and flocculation reactions are ensured to be sufficient, and the formed flocs achieve good separation during the settling stage.

[0017] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S4, the anaerobic / aerobic process is carried out in an anaerobic / aerobic tank, which includes an aerobic tank and an anoxic tank; the specific steps of the anaerobic / aerobic process include: S41. Adjust the pH of the electroplating wastewater to 7-8, add a carbon source to the electroplating wastewater, and then let it flow through the anoxic tank. S42. Aerate the aerobic section so that the electroplating wastewater flows through the aerobic tank; S43. After passing through the aerobic tank, the electroplating wastewater is returned to the anoxic tank until its denitrification rate remains unchanged, thus obtaining denitrified electroplating wastewater. The anoxic tank includes denitrifying bacteria; the aerobic tank includes nitrifying bacteria and aerobic bacteria; the carbon source includes one or more of glucose and sodium acetate; and the chemical oxygen demand / total nitrogen ratio of the electroplating wastewater in the anaerobic tank is ≥5.

[0018] This implementation method ensures the activity of denitrifying bacteria and achieves efficient nitrogen removal by controlling a suitable neutral pH and sufficient carbon source. When the chemical oxygen demand / total nitrogen ratio is too low, the carbon source for denitrification is insufficient, the nitrogen removal efficiency decreases significantly, and the total nitrogen in the effluent is likely to exceed the standard. Both excessively high and low pH will inhibit the activity of denitrifying and nitrifying bacteria, reducing the nitrogen removal efficiency.

[0019] In a preferred embodiment of the electroplating wastewater treatment method of the present invention, in step S41, the dissolved oxygen concentration in the anoxic zone is ≤0.2 mg / L; in step S42, the dissolved oxygen concentration in the aerobic zone is 2~4 mg / L; and in step S43, the reflux ratio is 100~300%. The anoxic zone maintains low dissolved oxygen to ensure smooth denitrification; the aerobic zone maintains high dissolved oxygen to promote nitrification and organic matter degradation.

[0020] Secondly, the present invention provides an electroplating wastewater treatment system, comprising a primary coagulation tank, a complex-breaking oxidation tank, a secondary coagulation tank, an anaerobic / aerobic tank, a membrane bioreactor tank, and a disinfection tank; in the electroplating wastewater treatment method according to any one of claims 1 to 9, step S1 is carried out in the primary coagulation tank; step S2 is carried out in the complex-breaking oxidation tank; step S3 is carried out in the secondary coagulation tank; and step S4 is carried out in the anaerobic / aerobic tank, the membrane bioreactor tank, and the disinfection tank.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a process of primary coagulation + complex-breaking oxidation + secondary coagulation to remove heavy metals from electroplating wastewater. Simultaneously, by combining anaerobic / aerobic processes and a bioreactor membrane, organic matter in the electroplating wastewater is removed, resulting in treated wastewater that meets discharge standards. Detailed Implementation

[0022] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0023] Unless otherwise specified, all other materials and reagents used in the examples are commercially available.

[0024] Example 1 One embodiment of the electroplating wastewater treatment method of the present invention is as follows: S1. The collected wastewater is introduced into the equalization tank to adjust the water quality and quantity. After equalizing the water quality and quantity, the wastewater is evenly sent into the primary coagulation tank.

[0025] S2. Add sodium hydroxide to the primary coagulation tank to adjust the pH to 9. Calculate the total amount of electroplating wastewater and add 600 ppm FeSO4. Stir evenly for 30 minutes, then add 60 ppm polyacrylamide, stir for 10 minutes, let stand for 20 minutes, filter, and introduce the electroplating wastewater into the complex breaking oxidation tank.

[0026] S3. Add sulfuric acid to the complex-breaking oxidation tank to adjust the pH to 2.5, add H2O2 solution, and calculate the total amount of electroplating wastewater as 800 ppm of H2O2. Stir evenly for 60 minutes to carry out the oxidation reaction, and then introduce the wastewater after complex-breaking oxidation into the secondary coagulation tank.

[0027] S4. Add sodium hydroxide to the secondary coagulation tank to adjust the pH to 8; based on the total amount of electroplating wastewater, add 600 ppm xanthate for precipitation reaction, then add 600 ppm polyferric sulfate and 60 ppm polyacrylamide, stir for 20 min, let stand for 10 min and filter, and introduce the electroplating wastewater into the anaerobic / aerobic tank.

[0028] S5. The anaerobic tank mainly contains hydrolytic acidifying bacteria, acetic acid-producing bacteria, and methanogenic bacteria, while the aerobic tank mainly contains nitrifying bacteria, polyphosphate-accumulating bacteria, and facultative aerobic bacteria. Sulfuric acid is added to the anaerobic tank to adjust the wastewater pH to 7.5. The dissolved oxygen levels in both the anaerobic and aerobic tanks are controlled by an aeration device, with the anaerobic tank at 0.15 mg / L and the aerobic tank at 3 mg / L. A carbon source, glucose, is added to the anaerobic tank to ensure that the electroplating wastewater COD / TN = 5. The anaerobic tank is equipped with equidistant biological elastic packing material with a diameter of 120 mm and made of polypropylene fiber. The aerobic tank is filled with special biological packing material to ensure full contact between the wastewater and the biofilm on the packing material under aerobic conditions. At the same time, the aerobic tank is equipped with a mixed liquor reflux device to return the electroplating wastewater to the anaerobic tank at a mixed liquor reflux ratio of 150%. After the denitrification rate remains constant, the wastewater is introduced into the membrane bioreactor tank.

[0029] S6. In the membrane bioreactor tank, aerobic microorganisms further remove organic matter from the wastewater, achieving sludge-water separation via the bioreactor membrane. The water from the membrane bioreactor tank is pumped to a disinfection tank, while the sludge is discharged into a sludge thickening tank.

[0030] S7. The disinfection tank uses sodium hypochlorite for disinfection at a concentration of 3 mg / L to obtain treated electroplating wastewater. The sludge in the sludge thickening tank is thickened and filtered, and the resulting wastewater is returned to the equalization tank for the next cycle.

[0031] Example 2 One embodiment of the electroplating wastewater treatment method of the present invention is as follows: S1. The collected wastewater is introduced into the equalization tank to adjust the water quality and quantity. After equalizing the water quality and quantity, the wastewater is evenly sent into the primary coagulation tank.

[0032] S2. Add sodium hydroxide to the primary coagulation tank to adjust the pH to 8. Calculate the total amount of electroplating wastewater and add 400 ppm FeSO4. Stir evenly for 30 minutes, then add 40 ppm polyacrylamide, stir for 10 minutes, let stand for 20 minutes, filter, and introduce the electroplating wastewater into the complex breaking oxidation tank.

[0033] S3. Add sulfuric acid to the complex-breaking oxidation tank to adjust the pH to 2, add H2O2 solution, and calculate the total amount of electroplating wastewater. The H2O2 dosage is 2000 ppm. Stir evenly for 60 minutes to carry out the oxidation reaction. Then, introduce the wastewater after complex-breaking oxidation into the secondary coagulation tank.

[0034] S4. Add sodium hydroxide to the secondary coagulation tank to adjust the pH to 9; based on the total amount of electroplating wastewater, add 400 ppm dithiocarbamate for precipitation reaction, then add 600 ppm polyferric sulfate and 60 ppm polyacrylamide, stir for 10 min, let stand for 15 min and filter, and introduce the electroplating wastewater into the anaerobic / aerobic tank.

[0035] S5. The anaerobic tank mainly contains hydrolytic acidifying bacteria, acetic acid-producing bacteria, and methanogenic bacteria, while the aerobic tank mainly contains nitrifying bacteria, polyphosphate-accumulating bacteria, and facultative aerobic bacteria. Sulfuric acid is added to the anaerobic tank to adjust the wastewater pH to 7. The dissolved oxygen levels in both the anaerobic and aerobic tanks are controlled by an aeration device, with 0.15 mg / L in the anaerobic tank and 2 mg / L in the aerobic tank. A carbon source, glucose, is added to the anaerobic tank to ensure that the electroplating wastewater COD / TN = 5. The anaerobic tank is equipped with equidistant biological elastic packing material with a diameter of 120 mm and made of polypropylene fiber. The aerobic tank is filled with special biological packing material to ensure full contact between the wastewater and the biofilm on the packing material under aerobic conditions. At the same time, the aerobic tank is equipped with a mixed liquor reflux device to return the electroplating wastewater to the anaerobic tank at a mixed liquor reflux ratio of 200%. After the denitrification rate remains constant, the wastewater is introduced into the membrane bioreactor tank.

[0036] S6. In the membrane bioreactor tank, aerobic microorganisms further remove organic matter from the wastewater, achieving sludge-water separation via the bioreactor membrane. The water from the membrane bioreactor tank is pumped to a disinfection tank, while the sludge is discharged into a sludge thickening tank.

[0037] S7. The disinfection tank uses sodium hypochlorite for disinfection at a concentration of 1 mg / L to obtain treated electroplating wastewater. After the sludge in the sludge thickening tank is thickened and filtered, the resulting wastewater is returned to the equalization tank for the next cycle.

[0038] Example 3 One embodiment of the electroplating wastewater treatment method of the present invention is as follows: S1. The collected wastewater is introduced into the equalization tank to adjust the water quality and quantity. After equalizing the water quality and quantity, the wastewater is evenly sent into the primary coagulation tank.

[0039] S2. Add sodium hydroxide to the primary coagulation tank to adjust the pH to 10. Calculate the total amount of electroplating wastewater and add 800 ppm FeSO4. Stir evenly for 30 minutes, then add 80 ppm polyacrylamide, stir for 10 minutes, let stand for 20 minutes, filter, and introduce the electroplating wastewater into the complex breaking oxidation tank.

[0040] S3. Add sulfuric acid to the complex-breaking oxidation tank to adjust the pH to 2, add H2O2 solution, and calculate the total amount of electroplating wastewater. The H2O2 dosage is 400 ppm. Stir evenly for 60 minutes to carry out the oxidation reaction. Then, introduce the wastewater after complex-breaking oxidation into the secondary coagulation tank.

[0041] S4. Add sodium hydroxide to the secondary coagulation tank to adjust the pH to 10. Calculate the total amount of electroplating wastewater and add 1000 ppm dithiocarbamate + xanthate + sodium sulfide (1:1:1) to carry out the precipitation reaction. Then add 1000 ppm polyferric sulfate and 100 ppm polyacrylamide, stir for 30 minutes, let stand for 5 minutes and filter. Then introduce the electroplating wastewater into the anaerobic / aerobic tank.

[0042] S5. The anaerobic tank mainly contains hydrolytic acidifying bacteria, acetic acid-producing bacteria, and methanogenic bacteria, while the aerobic tank mainly contains nitrifying bacteria, polyphosphate-accumulating bacteria, and facultative aerobic bacteria. Sulfuric acid is added to the anaerobic tank to adjust the wastewater pH to 8. The dissolved oxygen levels in both the anaerobic and aerobic tanks are controlled by an aeration device, with 0.15 mg / L in the anaerobic tank and 3.5 mg / L in the aerobic tank. A carbon source, glucose, is added to the anaerobic tank to ensure that the electroplating wastewater COD / TN = 5. The anaerobic tank is equipped with equidistant biological elastic packing material with a diameter of 120 mm and made of polypropylene fiber. The aerobic tank is filled with special biological packing material to ensure full contact between the wastewater and the biofilm on the packing material under aerobic conditions. At the same time, the aerobic tank is equipped with a mixed liquor reflux device to return the electroplating wastewater to the anaerobic tank at a mixed liquor reflux ratio of 150%. After the denitrification rate remains constant, the wastewater is introduced into the membrane bioreactor tank.

[0043] S6. In the membrane bioreactor tank, aerobic microorganisms further remove organic matter from the wastewater, achieving sludge-water separation via the bioreactor membrane. The water from the membrane bioreactor tank is pumped to a disinfection tank, while the sludge is discharged into a sludge thickening tank.

[0044] S7. The disinfection tank uses sodium hypochlorite for disinfection at a concentration of 5 mg / L to obtain treated electroplating wastewater. The sludge in the sludge thickening tank is thickened and filtered, and the resulting wastewater is returned to the equalization tank for the next cycle.

[0045] Comparative Example 1 This invention provides a comparative example of an electroplating wastewater treatment method. The only difference between this comparative example and Example 1 is that in step S4, no metal scavenging agent is added. The other steps and parameters are the same as in Example 1.

[0046] Comparative Example 2 This invention provides a comparative example of an electroplating wastewater treatment method. The difference between this comparative example and Example 1 is that the primary coagulation in step S2 and the complex-breaking oxidation in step S3 are omitted. The other steps and parameters are the same as in Example 1.

[0047] Comparative Example 3 This invention provides a comparative example of an electroplating wastewater treatment method. The difference between this comparative example and Example 1 is that step S5 (anaerobic / aerobic process) is omitted. The other steps and parameters are the same as in Example 1.

[0048] Comparative Example 4 This invention provides a comparative example of an electroplating wastewater treatment method. The difference between this comparative example and Example 1 is that the primary coagulation in step S2 is omitted, while the other steps and parameters are the same as in Example 1.

[0049] The water quality of electroplating wastewater and the treatment results of electroplating wastewater in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1. The testing standards for chemical oxygen demand (COD) are as follows: "Determination of Chemical Oxygen Demand in Water - Dichromate Method" (HJ 828-2017); total nitrogen is tested according to "Determination of Total Nitrogen in Water - Alkaline Potassium Persulfate Digestion Ultraviolet Spectrophotometric Method" (HJ 636-2012); total phosphorus is tested according to "Determination of Total Phosphorus in Water - Ammonium Molybdate Spectrophotometric Method" (GB 11893-89); ammonia nitrogen is tested according to "Determination of Ammonia Nitrogen in Water - Nessler's Reagent Spectrophotometric Method" (HJ 535-2009); suspended solids are tested according to "Determination of Suspended Solids in Water - Gravimetric Method" (GB 11901-89); and total copper is tested according to "Determination of Copper, Zinc, Lead, and Cadmium in Water - Atomic Absorption Spectrophotometric Method" (GB 11901-89). 7475-87); The test standard for total nickel is "Determination of Nickel in Water by Flame Atomic Absorption Spectrophotometry" (GB 11912-89).

[0050] Table 1 As shown in Table 1, the combination of the primary coagulation + complex-breaking oxidation + secondary coagulation process of this invention with the anaerobic / aerobic + membrane bioreactor process greatly improves wastewater treatment efficiency. Each step is interconnected and indispensable. After treatment, the pollutants and heavy metal ions in the electroplating wastewater are significantly reduced, meeting the discharge standards.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for treating electroplating wastewater, characterized in that, Includes the following steps: S1. Adjust the pH of the electroplating wastewater to 8-10, add ferrous sulfate and stir for the first time, add flocculant and stir for the second time, let it stand and then filter. S2. Adjust the pH of the electroplating wastewater to 2-3, add an oxidant and stir for the third time; the oxidant includes hydrogen peroxide. S3. Adjust the pH of the electroplating wastewater to 7-9, add metal capture agent, coagulant and flocculant and stir for the fourth time, let it stand and then filter. S4. The filtered electroplating wastewater is subjected to anaerobic / aerobic denitrification treatment, followed by membrane separation and filtration in a bioreactor, and then disinfection to obtain the treated electroplating wastewater.

2. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S1, the first stirring time is 25-35 minutes, the second stirring time is 10-15 minutes, and the settling time is 15-25 minutes.

3. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S1, the flocculant includes one or more of polyacrylamide and chitosan; the amount of ferrous sulfate added is 400-800 ppm based on the total amount of electroplating wastewater; the amount of flocculant added is 400-800 ppm.

4. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S2, the third stirring time is 50-70 minutes.

5. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S2, the amount of oxidant added is 400~2000 ppm, calculated based on the total amount of electroplating wastewater.

6. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S3, the metal scavenging agent includes one or more of xanthate, dithiocarbamate, and sodium sulfide; the coagulant includes one or more of ferrous sulfate, ferric sulfate, ferric chloride, aluminum sulfate, aluminum chloride, polyferric sulfate, polyaluminum chloride, and polyaluminum ferric chloride; the flocculant includes polyacrylamide; the amount of metal scavenging agent added is 400-1000 ppm based on the total amount of electroplating wastewater; the amount of coagulant added is 200-1000 ppm; and the amount of flocculant added is 20-100 ppm.

7. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S3, the fourth stirring time is 10-30 min, and the settling time is 5-15 min.

8. The electroplating wastewater treatment method as described in claim 1, characterized in that, In step S4, the anaerobic / aerobic process is carried out in an anaerobic / aerobic tank, which includes an aerobic tank and an anoxic tank. The specific steps of the anaerobic / aerobic process include: S41. Adjust the pH of the electroplating wastewater to 7-8, add a carbon source to the electroplating wastewater, and then let it flow through the anoxic tank. S42. Aerate the aerobic section so that the electroplating wastewater flows through the aerobic tank; S43. After passing through the aerobic tank, the electroplating wastewater is returned to the anoxic tank until its denitrification rate remains unchanged, thus obtaining denitrified electroplating wastewater. The anoxic tank includes denitrifying bacteria; the aerobic tank includes nitrifying bacteria and aerobic bacteria; the carbon source includes one or more of glucose and sodium acetate; and the chemical oxygen demand / total nitrogen ratio of the electroplating wastewater in the anaerobic tank is ≥5.

9. The electroplating wastewater treatment method as described in claim 8, characterized in that, In step S41, the dissolved oxygen concentration in the anoxic tank is ≤0.2 mg / L; in step S42, the dissolved oxygen concentration in the aerobic tank is 2~4 mg / L; and in step S43, the reflux ratio is 100~300%.

10. An electroplating wastewater treatment system, characterized in that, The method includes a primary coagulation tank, a complex-breaking oxidation tank, a secondary coagulation tank, an anaerobic / aerobic tank, a membrane bioreactor tank, and a disinfection tank; in the electroplating wastewater treatment method according to any one of claims 1 to 9, step S1 is carried out in the primary coagulation tank; step S2 is carried out in the complex-breaking oxidation tank; step S3 is carried out in the secondary coagulation tank; and step S4 is carried out in the anaerobic / aerobic tank, the membrane bioreactor tank, and the disinfection tank.

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